The present invention relates to a control device for an internal combustion engine.
The internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2004-150302 includes an intake passage coupled to coupling pipes. The coupling pipes include, for example, a positive crankcase ventilation (PCV) passage, which cause blow-by gas that is generated in a crank chamber of the internal combustion engine to flow into the intake passage. The internal combustion engine also includes an idle speed control device. The idle speed control device controls the amount of intake air introduced to combustion chambers so that the idle speed becomes equal to a target rotational speed.
The control device for an internal combustion engine disclosed in the above publication detects the coupling state between the coupling pipes and the intake passage during an idling operation of the internal combustion engine. If any of the coupling pipes is detached from the intake passage, air flows into the intake passage through a coupling port that has been opened. Thus, the rotational speed and the air-fuel ratio of the internal combustion engine are changed. The changes are reflected in the correction amount of the idle speed control device that reflects the change amount of the rotational speed of the internal combustion engine. Thus, the control device detects whether any of the coupling pipes is detached from the intake passage based on the correction amount of the idle speed control device.
Some of the internal combustion engines include, as the coupling pipes, a fresh air passage that causes fresh air to flow into the crank chamber from the intake passage in accordance with the flow of the blow-by gas through the PCV passage. In a case in which the control device disclosed in the above publication is applied to such an internal combustion engine to detect whether the fresh air passage is detached from the intake passage, the area of the coupling port between the fresh air passage and the intake passage needs to be increased so that the operating state of the internal combustion engine changes in accordance with the increase in the intake air amount due to the detachment of the fresh air passage. In this case, the design of the internal combustion engine needs to be changed.